posted April 13, 2006 09:21 AM               

A large screw can conduct heat easily axially from the melting zone to into the solids conveying zone. So, by just making the screw hollow (cuts down on the area for axial heat conduction), some improvement could be acheived. This can work well for amorphous materials, too. If need be, air cooling can be added.

One just needs to be sure that the hollow screw can carry the torque needed. This becomes difficult in screws smaller than 63 mm. However, your screw is large enough that you can make it hollow in the solids section by a significant amount.

steve@extrudertech.com

posted April 13, 2006 08:50 PM               

Use bulk density for PP at some nominal pressure (10 MPa), if you can get it. If you have other machines with PP, check the angle for them, too. The angle should always be very close if the machines are running well and the screws are of one type(i.e. single stage, barrier, or two-stage, etc.) Likely, the angle is between 3 and 7 degrees. Screw size, channel depth, speed have little effect on solids angle. If your angle is low, then you can suspect that there is room for improvement.

You can learn about the solids conveying angle at http://www.extrudertech.com/KinematicsofSolidsConveyingNotes.pdf This is slides with notes on the solids conveying angle and the kinematics model for solids conveying.

steve@extrudertech.com